[sdiy] CA3080 switch driving voltage

[jhaible]

> > 60mV - much lower than I expected.
> > Doesn't this mean that there is a temperature drift from the diff pair
> > still working in the "almost linear" area?
> > But anyway - if saturation must be avoided, then this is the way to go.
> > Probably compensating for the tempco somewhere else. (I remember
> > there was another EN article with diodes setting the thresholds of
> > the schmitt trigger - maybe this was exactly for that reason.)
>
> Are you referring to this? From an RCA ap-note. Response is only 45 ns,
with
> 1 ma. See:
>
> http://www.musicsynthesizer.com/DIY/Grant/OTA.html

No. But the schmitt trigger it refers to is also used in that VCO.


> > Thanks for pointing this out. All my previous triangle cores show
> > the effect you describe in EN#112. Not tracking ore than 3 octaves
> > accurately, and HFT trimmers won't help. This time I'll try the 60mV.
>
> I'm using just a 100K in series with the NJM13700 input. It will zener at
> around 7 volts. Works OK for an LFO, I'll have to see how it tracks as a
> VCO.

LFO is no problem. Even a freqzency range from 1/(10 minutes) to 10kHz
is no problem. Precise tracking as a VCO, over more than 3 octaves is
difficult,
though.

Using the diff pair transistors as zener might degrade the chip over time.
Probably no problem in a LFO either, but I wouldn't use the same chip
for a VCF later. (Maybe this is just paranoia, but it exceeds the
maximum rating specs.)

JH.